Duva’s attorney, Patrick English, claims in the lawsuit, filed Tuesday in U.S. District Court in New York, that the defendants interfered in an agreed-upon light-heavyweight title unification bout between Michel’s fighter, World Boxing Council champion Adonis Stevenson (23-1, 20 knockouts), and Duva’s World Boxing Organization champion, Sergey Kovalev (24-0-1, 22 KOs).

The lawsuit contends that after Stevenson and Kovalev won showcase bouts against other opponents Nov. 30 on HBO, Duva and Michel struck a co-promotion agreement by email Jan. 23.

After Duva wrote to Michel that the terms were acceptable, the lawsuit alleges, Michel emailed back that “We also have a deal on our side!! … Let’s make a good sale to HBO.”

A day later, the complaint alleges, an HBO executive offered Duva and Michel a $2.4-million rights fee and “there was a consummated agreement for a co-promotion.”

Duva, in a telephone conversation with The Times on Wednesday, said, “It was a done deal. … Yvon represented his fighter had agreed to it and I represented to him that my fighter had agreed to it. That’s a deal. We have the right to sign the fighters, that’s what we do.”

That agreement, Duva said, remained upheld by Michel into March, with Duva’s company on Feb. 18 sending Michel a letter expressing concern over the reported involvement of Haymon with Stevenson.

In recent weeks, reports of Schaefer’s strained relationship with Golden Boy President and majority shareholder Oscar De La Hoya have raised speculation that Schaefer and Haymon are moving toward a business venture together. Duva’s lawsuit claims Haymon and Schaefer are working to “wrest control” of Golden Boy.

The lawsuit alleges Haymon, operating with Schaefer and Showtime Vice President Stephen Espinoza, began moving toward another bout for Stevenson in the fall against 49-year-old Bernard Hopkins.

Haymon and Schaefer “have obviously got some kind of agenda and everything, including my rights and the fans’ ability to see the fights they want to see, and in some instances the rights of fighters not attached to them are being trampled on,” Duva said in the interview. “I’m not going to take it anymore.”

Schaefer, reached by telephone in Las Vegas, where he's promoting Saturday night's Mayweather-Marcos Maidana welterweight world title fight, said he’s “not worried about” the lawsuit because Golden Boy currently has no deal in place with Stevenson.

“That’s no secret that I’m interested in pursuing a Stevenson fight for Bernard, because he wants to unify the titles, but I have nothing to do with Stevenson now.… He has a fight [against Andrzej Fonfara on May 24 in Montreal] that I’m not involved with.

“It seems farfetched. Kathy Duva … I haven’t dealt with her in I don’t know how long. She’s made it clear she’s loyal to HBO. I respect her for that. I’m loyal to Showtime. I don’t understand what her problem is.”

A Haymon representative declined to comment about the lawsuit and a Showtime publicist had no comment.

Duva’s lawsuit alleges Haymon is operating as a manager and promoter in violation of the federal Muhammad Ali Act. The lawsuit claims Showtime made an offer to Stevenson for a Hopkins fight that exceeded the HBO Kovalev offer and had “the clear intent of disrupting the Stevenson/Kovalev bout.”

Duva said the lawsuit seeks general and punitive damages in millions of dollars.

“Those damages are used in the legal system as a deterrent for people who don’t want to follow the rules,” Duva said in the interview. “They didn’t follow the rules. People should be called on that, and this is going to create an opportunity for people to more closely scrutinize what’s going on with these powerful people who seem to have convinced everyone they have some mystical properties that allow them to do things that other people don’t.

“It’s going to be very interesting. People have a lot of questions, they may get some answers here.”